Architecturally, is it normal to have multiple canvas in your scene?

Without going into a lot of boring detail. Is it acceptable to have multiple Canvas in your scene? The biggest reason I'm wanting multiple is because each thing I want on the canvas does a different thing. Like, displaying images, fading alpha, playing video. Each needs the ability to be displayed and hidden.

You want to group items in canvases so that the group is getting updated as a whole whenever possible without updating anything else. For instance, if your resource calculations run once per second in your RTS, you want to update your header's resource counts all at once and also have those separate from a canvas that updates when the player interacts with it. Also make sure you turn off raycasting for any UI elements that don't require it, which can degrade performance, especially on mobile.

Important reminder: Whenever any drawable UI element on a given Canvas changes, the Canvas must re-run the batch building process.

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This isn't just when you activate or deactivate a GameObject or change the content of a Text element, but also every single frame if it has an active Animator. The guide has tips for avoiding these issues, such as using a tween script instead of Animator, and disabling canvases efficiently.